1. Field of the Invention
The present invention relates to a semiconductor laser device and method for manufacturing the same, and more specifically to a buried semiconductor laser device and method for manufacturing the same.
2. Background Art
With the expansion of optical fiber communications network in recent years, demands for semiconductor laser devices that enable high-speed operation at high temperatures have been increasing. As a product to realize such demands, a semiconductor laser device using an AlGaInAs-based material for an active layer is attracting attention.
Since Al-containing semiconductor materials are easily oxidized, oxides of Al are easily formed in such semiconductor materials. If electric current is injected into the active layer of such a semiconductor laser, the defects formed by the oxides of Al create non radiative recombination centers to deteriorate the device. Therefore, a semiconductor laser wherein an AlGaInAs-based material is applied in a multiple quantum well (MQW) active layer has been fabricated using a structure and method for preventing the oxidation of AlGaInAs.
In Non-Patent Document “Japanese Journal of Applied Physics, Vol. 43, No. 10A, pp. L1247-L1249”, a method for manufacturing a semiconductor laser that prevents the oxidation of AlGaInAs is disclosed. The manufacturing method will be described below.
First, an n-type InP clad layer, a lower light confinement layer, an MQW active layer, an upper light confinement layer, and a p-type InP clad layer are sequentially laminated on an n-type InP substrate in the order from the bottom. These layers are formed by a metal organic vapor phase epitaxy (MOVPE) method or the like. The lower light confinement layer, the MQW active layer, and the upper light confinement layer are formed using an AlGaInAs-based material.
Next, a mask pattern is formed on the p-type InP clad layer, and is used as a mask to etch the p-type InP clad layer, the upper light confinement layer, the MQW active layer, the lower light confinement layer, and the n-type InP clad layer. As a result, forward tapered mesa side surfaces are formed on both sides of the mask pattern. Then, a buried layer is formed along the mesa side surfaces. Next, the mask pattern is removed to form a p-type InP clad layer on the entire surface.
In the above-described manufacturing method, the etching step to form the mesa side surfaces is carried out using HCl gas in a reactor of metal organic chemical vapor deposition (MOCVD) equipment. Furthermore, in the same reactor, a buried layer is formed. Specifically, in the same reactor of the same equipment, the formation of mesa side surfaces and the formation of a buried layer can be sequentially performed.
By thus forming the layers, the oxidation of AlGaInAs exposed on the mesa side surfaces can be prevented.